Molecular engineering in Perovskite solar cell

This ppt is about perovskite solar cells

1. Molecular engineering of contact interfaces for high-performance perovskite solar cell

2. Problems associated with perovskite /metal oxide interface Non radiative recombination. Impedes charge carriers transfer. Undesirable chemical reactions during the operation process. Mechanical stability issues. Combined these issues badly effect both the optical and electrical properties of PSCs.

3. Ionic nature of perovskite Various defect states due to ionic nature of perovskite Issues: Deep defect states Non radiative recombination Hysteresis issues in J-V curve Charge trapping These all issues reduces the PCE of PSCs

4. Metal oxides common choices of ETL Cause defect on their surface due to the uncoordinated surface atoms results in deep states. When interface with semiconductor ( Perovskite ) increase charge carrier recombination and also reduces transfer and collection of charges. For example: Interfacial Fermi level pinning effect,and Schottky barriers.

5. Chemical instability of Perovskite The active layer is in direct contact with metal oxide via chemical, which may react and degrade.

6. Mechanical stress Mechanical stress also alter the performance of PSCs. Such stress may come due to mismatch of the coefficient of thermal expansion of different layers.

7. Fermi level pinning effect Fermi level pinning is a hot spot in the field of semiconductor science and technology. The Fermi level pinning effect is an important concept in semiconductor physics. Originally, the Fermi level in semiconductors is prone to position changes. For example, doping the donor impurity can move the Fermi energy level to the bottom of the conduction band, and the semiconductor becomes an n-type semiconductor; doping the acceptor impurity can make the Fermi energy level move to the top of the valence band, and the semiconductor becomes a p-type semiconductor. However, if the position of the Fermi level cannot change due to doping, etc., then this situation is called the Fermi level pinning effect. When this effect works, even if a lot of donors or acceptors are doped into the semiconductor, they cannot be activated (that is, they cannot provide carriers), so the type of the semiconductor cannot be changed, so it is difficult to make it through impurity compensation. Out of the pn junction. The reason for the Fermi level pinning effect is related to the nature of the material. Wide bandgap semiconductors ( GaN , SiC , etc.) are a typical example. Generally, such semiconductors can only be prepared as n-type or p-type semiconductors, and their type cannot be changed by doping (that is, the Fermi energy level cannot be moved), so it is called Unipolar semiconductor. Generally, semiconductors with strong ionic properties (such as II-VI semiconductors, CdS , ZnO , ZnSe , CdSe ) are often unipolar semiconductors. This is mainly due to the existence of a large number of charged defects, which make the Fermi level pinned. Because of this, when GaN is used to make blue-emitting diodes, it has previously encountered great difficulties. Later, the doped donor or acceptor impurities were activated through special annealing measures, and a pn junction was obtained—— Diodes that emit blue light. Amorphous semiconductors also often have Fermi level pinning effects. Most of the produced amorphous semiconductors are high-resistance materials, and the Fermi energy level cannot be moved due to doping, which is also due to the large number of defects in it.

8. Solutions: To design new multifunctional double sided passivation methods. Which can help to passivate surface defects both side of metal oxide and perovskite interface. The interfacial engineering break the direct contact of perovskite and metal oxide via double sided interfacial passivation layer and acts as a stable barrier layer. It means the interfacial layer physically separate the perovskite layer from metal oxide, which helps to stop the undesireable chemical reactions at the interface and thus improve the chem stability.

9. Best method molecular interface engineering To passivate and link both perovskite and metal oxide layer interfaces.